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+# General Concepts
+
+
+## Data Model
+
+### Dataset
+
+In the context of xcube, a _dataset_ is a container for spatial
+gridded data [variables](#Variable) that usually share the same
+coordinate reference system, the same dimensions, and therefore 
+the same grid.
+Besides the data variables, a dataset also provides metadata such 
+as the spatio-temporal coverages, the type of coordinates, and information
+about the content.
+A dataset can be associated with [places](#Place) that are
+organised in [place groups](#Place-Group).
+
+Datasets that provide variables with two spatial dimensions and a time
+dimension are also referred to as _data cubes_. Hence, the data cubes 
+supported by the viewer are 4-D: variable, time, y, and x.
+The viewer may support also other data cube dimensions in the future. 
+
+The list of available datasets is usually fixed for a deployed viewer
+application instance. One of the datasets is the viewer's 
+[selected dataset](#Selected-Dataset).
+
+### Variable
+
+A _variable_ provides n-dimensional, gridded, geospatial data.
+Every variable has a name, a numeric data type, and two spatial dimensions.
+Usually, variables are 3-D and also have a time dimension that can be of 
+variable length. Each time step along the dimension determines an individual 
+2-D spatial image of the 3-D variable and is associated with a given timestamp.
+
+### Place
+
+### User Place
+
+### Place Group
+
+## Selections
+
+### Selected Dataset
+
+The selected dataset determines the set of selectable [variables](#Variable)
+and the possible range of the currently [selected time](#Selected-Time).
+
+The newly [selected variable](#Selected-Variable)
+the variable with the same name as the previously selected variable, given
+that is exists. Otherwise, the newly selected dataset's first variable will
+be selected.
+
+### Selected Variable
+
+The selected variable is the one shown in the map, given that the
+[variable layer](#Variable-Layer) is visible.
+
+If a [place](#Places-and-Place-Groups) is selected [vector geometry]()
+
+### Pinned Variable
+
+### Selected Place
+
+### Selected Place Group
+
+### Selected Time
+
+
+## Layers
+
+### Variable Layer
+
+The _variable layer_ is the top-most gridded data layer in the map.
+It overlays the [dataset RGB layer](#Dataset-RGB-Layer).
+
+### Dataset RGB Layer
+
+### Basemaps and Overlays